Subs firing nuclear cruise missiles, to be more specific. All the participants have realized that traditional navies just don't have the sex appeal of submarines that can go anywhere and get away with nearly anything, vastly increasing the unpredictability of victory in such a war and vastly decreasing warning times for civilians.
Improvements in stealth systems for submarines make the worst case scenarios also the most attractive ... creeping up on the coast of your enemy with a fleet of subs and launching nuclear cruise missiles into the interior traveling at twenty times the speed of sound. Warning systems for military response become almost impossible and early warning systems for civilians become completely impossible. The scenario always ends the same way - having to absorb a first strike and then retaliating. To absorb a first strike, your country has to adopt a defensive posture that means nuclear defense is a way of life, so they are always in situations where they or their equipment can quickly be sheltered. This was what Eisenhower had in mind with the Federal Highway System (the original plan had a super shelter built into every overpass) and Kennedy was planning to implement if he had not been triangulated in Dallas.
It takes about twenty years to get a decent civil defense program going, another twenty years to finish it and twenty years of regular maintenance and drills to keep it running. So far the Kwanstain is running about sixty years behind in all regards. The sum of the nuclear defense posture in the Kwa is to grin ear-to-ear sweating and hope for the best. Vault-Co calls it the Eternally Sunny Disposition of the Walking Dead.